Habitable zone super-earth exoplanet found

[TimothyC]

'Super-Earth' Alien Planet May Be Habitable for Life
by Mike Wall, SPACE.com Senior Writer
Date: 07 November 2012 Time: 07:02 PM ET

stronomers have detected an alien planet that may be capable of supporting life as we know it — and it's just a stone's throw from Earth in the cosmic scheme of things.

The newfound exoplanet, a so-called "super-Earth" called HD 40307g, is located inside its host star's habitable zone, a just-right range of distances where liquid water may exist on a world's surface. And the planet lies a mere 42 light-years away from Earth, meaning that future telescopes might be able to image it directly, researchers said.

"The longer orbit of the new planet means that its climate and atmosphere may be just right to support life," study co-author Hugh Jones, of the University of Hertfordshire in England, said in a statement. "Just as Goldilocks liked her porridge to be neither too hot nor too cold but just right, this planet or indeed any moons that it has lie in an orbit comparable to Earth, increasing the probability of it being habitable."

HD 40307g is one of three newly discovered worlds around the parent star, which was already known to host three planets. The finds thus boost the star's total planetary population to six. [Video: Super Earth May Have Liquid Water]

Finding new signals in the data

The star HD 40307 is slightly smaller and less luminous than our own sun. Astronomers had previously detected three super-Earths — planets a bit more massive than our own — around the star, all of them in orbits too close-in to support liquid water.

In the new study, the research team re-analyzed observations of the HD 40307 system made by an instrument called the High Accuracy Radial velocity Planet Searcher, or HARPS.

HARPS is part of the European Southern Observatory's 11.8-foot (3.6 meters) telescope at the La Silla Observatory in Chile. The instrument allows astronomers to pick up the tiny gravitational wobbles an orbiting planet induces in its parent star.

The researchers' new analysis techniques enabled them to spot three more super-Earths around the star, including HD 40307g, which is thought to be at least seven times as massive as our home planet.

HD 40307g may or may not be a rocky planet like Earth, said study lead author Mikko Tuomi, also of the University of Hertfordshire.

"If I had to guess, I would say 50-50," Tuomi told SPACE.com via email. "But the truth at the moment is that we simply do not know whether the planet is a large Earth or a small, warm Neptune without a solid surface."

A jam-packed extrasolar system

HD 40307g is the outermost of the system's six planets, orbiting at an average distance of 56 million miles (90 million kilometers) from the star. (For comparison, Earth zips around the sun from about 93 million miles, or 150 million km, away.)

The other two newfound exoplanets are probably too hot to support life as we know it, researchers said. But HD 40307g — which officially remains a "planet candidate" pending confirmation by follow-up studies — sits comfortably in the middle of the star's habitable zone.

Further, HD 40307g's orbit is distant enough that the planet likely isn't tidally locked to the star like the moon is to Earth, researchers said. Rather, HD 40307g probably rotates freely just like our planet does, showing each side of itself to the star in due course.

The lack of tidal locking "increases its chances of actually having Earth-like conditions," Tuomi said.

The new study has been accepted for publication in the journal Astronomy & Astrophysics.

Very cool.

[Lord Zentei]

At 42 light years, shouldn't Hubble be able to image it directly? Yet they speak of "future telescopes".

PS:
Apparently, the number of known exoplanet systems now numbers 665. So this would make HD 40307 the 666th solar system overall that's known to exist. And it's in the habitable zone.

[TimothyC]

At 42 light years, shouldn't Hubble be able to image it directly? Yet they speak of "future telescopes".

PS:
Apparently, the number of known exoplanet systems now numbers 665. So this would make HD 40307 the 666th solar system overall that's known to exist. And it's in the habitable zone.

Except HD40307 was already known to as having exoplanets prior to this.

[Lord Zentei]

Except HD40307 was already known to as having exoplanets prior to this.

Ah, well. It was just an off-hand joke, anyway.

But regarding the more serious question I asked - is there any reason existing telescopes can't image it?

[Eternal_Freedom]

Even the Hubble can't see something as relatively small as a planet when it's near a star. The star, being waaaaay more luminous, dominates the image meaning planets (which only reflect light) can't be seen. Same reason why you can't see faint stars near the full moon, the brighter object washes out the dimmer ones. This is why we find exoplanets using stuff like HARPS or by measuring the tiny dip in brightness as a planet passes in front of the star.

I think by "future telescopes" they mean James Webb. When that baby finally gets launched Hubble will look like a pocket camera in comparison.

[Lord Zentei]

I am actually fairly well versed in the basics of these things.

But I asked because I recalled that direct imaging of exoplanets has been achieved before now. On review, however, they are all located in significantly larger orbits.

[Eternal_Freedom]

I am actually fairly well versed in the basics of these things.

But I asked because I recalled that direct imaging of exoplanets has been achieved before now. On review, however, they are all located in significantly larger orbits.

My apologies if I sounded condescending. Yes, direct imaging has been done for large planets far out, but IIRC "Direct imaging" means they show up as a "star" that moves across several images. Just like how we see asteroids.

[Lord Zentei]

IIRC "Direct imaging" means they show up as a "star" that moves across several images. Just like how we see asteroids.

Yes, I'm well aware, unfortunately. Still, it gives far more potential for information than the more basic methods.

[Eternal_Freedom]

IIRC "Direct imaging" means they show up as a "star" that moves across several images. Just like how we see asteroids.

Yes, I'm well aware, unfortunately. Still, it gives far more potential for information than the more basic methods.

And the mere fact that we can image planets in another damn solar system is just plain awesome.

[Guardsman Bass]

The planet in question could be anything between 4.5 and 9.7 Earth masses. If we could find its radius, then we could determine whether it's a big rocky planet or a small "gas dwarf" (or even an oceanic world).

In any case, it's good news. I wonder if Kepler is capable of confirming the discovery and finding the radius.

[khursed]

The james webb telescope won't be great for taking pictures of planet as it will be an infra-red telescope.

Hopefully, NASA will have funding for it, then later funding for a replacement for the hubble in normal light wavelength.

[starslayer]

The james webb telescope won't be great for taking pictures of planet as it will be an infra-red telescope.

Hopefully, NASA will have funding for it, then later funding for a replacement for the hubble in normal light wavelength.

On the contrary, JWST is better for observing planets. Earth's thermal emission, for example, peaks at around 10 microns; if you want the best chance at observing an Earth-like planet, you should try and observe at that sort of wavelength if at all possible, since that makes your contrast problem smaller. Higher resolution is fairly easy to get in this case.

A straight replacement for Hubble probably will not be forthcoming. The atmosphere is very transparent at optical wavelengths. While resolution does suffer due to atmospheric effects, and stupid-accurate Kepler-style photometry is not possible from the ground due to unpredictably changing atmospheric conditions, you can build a 10 or even a 30 m mirror for a ground-based telescope. You can't even get close to that for a space mission, at least not without absolutely staggering costs. It is a better use of available money and science time/effort to only build optical space telescopes for specific missions that aboslutely require space, such as Kepler, Gaia (parallaxes), etc, precisely because the atmosphere is so transparent to visible light. This is usually because of the required long-term resolution or photometry accuracy. Adaptive optics can make up the resolution difference for just about everything else.

In any case, it's good news. I wonder if Kepler is capable of confirming the discovery and finding the radius.

Unfortunately, no. The planet probably doesn't transit its star in the first place (it was found by HARPS, a radial velocity instrument), nor is it anywhere near the Kepler field. For various reasons, Kepler will not be repointed from its current field at any point during the mission lifetime.

[Sea Skimmer]

Not only can you build huge optics on the ground, you can combined them together now to effectively create optical apertures that are physically impossible with any one telescope. Its also vastly cheaper to operate a ground telescope then one in space, an under looked cost of space missions. Hubble would have never lasted so long, ignoring the unplanned repair mission, without billions in service missions. It total program cost was some 10 billion dollars. In contrast as far as I can tell the best optical ground telescope now is the Large Binocular Telescope, and it only cost 120 million dollars to build. Now imagine we built five of them on the same site and used them as one.

[Guardsman Bass]

Unfortunately, no. The planet probably doesn't transit its star in the first place (it was found by HARPS, a radial velocity instrument), nor is it anywhere near the Kepler field. For various reasons, Kepler will not be repointed from its current field at any point during the mission lifetime.

I'm sad to hear that, but I guess it's not surprising.

You mentioned that resolution is limited when using ground telescopes. Does that mean you can't direct image planets even with large ground telescopes or telescope arrays?

[starslayer]

Actually, you very much can; most of the planets found by direct imaging have come from ground-based surveys. Adaptive optics (AO) is killer; the small well-corrected fields AO gives you are not a problem when all your spearations are arcseconds or less*. There are several techniques that are used in tandem with AO to get direct images of planets, such as angular differential imaging and coronographs. As was mentioned up thread, though, all we've been able to do so far is very large planets/companions far from their stars. As AO continues to get better, and the 30 m class instruments are built, we'll be able to dive much closer in to the parent star and image yet smaller planets.

*Hubble's main advantage besides photometry at this point is that it's entire field is at full resolution, and that that resolution is steady and will not change over the lifetime of the telescope. Since the atmosphere changes from night to night and second to second (this is why stars twinkle, and it royally screws with astronomical images; LBT operates at about 1% resolution effectiveness without AO most nights), the effectiveness of AO changes on those timescales too. Additionally, AO can't yet give you several arcminute wide corrected fields. This means that projects which require very high and steady angular resolution should be done from space. Those only requiring the first (which turns out to be most things) can now be fairly easily done from the ground.